Currently, a part made of a sintered ceramic is re-oxidized by being treated in oxygen at low temperature (about 450.degree. C.), or else the part is cooled very slowly in oxygen just after it has been sintered.
The article by N. Mc. N. Alford et al published in Nature vol. 332, on Mar. 3, 1988, pages 58-59, indicates that the current density that can be passed through a part made of a ceramic, such as YBa.sub.2 Cu.sub.3 O.sub.7-.delta., depends to a large extent on the oxygen content. The authors advocate making .delta. as close as possible to zero.
The article by T. B. Lindemer et al published in the J. Am. Ceram. Soc. 72 (10) 1775 88 (1989) specifies the relationships between .delta. and various treatment parameters such as temperature and the partial pressure of oxygen in the atmosphere used. It would seem possible to achieve values for .delta. not greater than 0.01, by means of treatment in oxygen at temperatures of less than 400.degree. C., if thermodynamic equilibrium is reached. But thermodynamic equilibrium can only be reached after a very long time.
The publication by J. M. Heintz et al in J. Less Common Metals 164-165 (1990) p. 337 shows that there are diffusion barriers at the interfaces between the grains of the ceramic, and this considerably reduces oxidation speeds. The authors propose increasing the kinetics and the diffusion by increasing the temperature. But, in pure oxygen at 500.degree. C., values for .delta. are obtained that are greater than or equal to 0.03.
An object of the present invention is to provide a method of treatment that enables oxygen diffusion to be activated and the value of .delta. to be reduced with treatment of reasonable duration.